Radio infrared apparatus

ABSTRACT

Error detection section  109  carries out error detection using demodulated data and outputs an error rate to SIR versus error rate estimation section  110.  SIR versus error rate estimation section  110  estimates an SIR versus error rate and outputs the result of decision as to whether the correction of the target SIR value is necessary or not to target SIR correction section  111.  Target SIR correction section  111  corrects the target SIR value based on the decision result. The information on the demodulation capability of a BTS is output to G parameter control section  112  and G parameter control section  112  determines an optimal gain factor. A G parameter indicating the determined gain factor is output to multiplexing section  107  of the BTS. The G parameter is output to SIR versus error rate estimation section  110.  This makes it possible to perform communications with an optimal gain factor and target SIR during diversity handover between base stations with and without an interference canceller or between base stations with interference cancellers of different capabilities.

TECHNICAL FIELD

[0001] The present invention relates to a digital radio communicationsystem, and more particularly, to a radio infrastructure apparatus in aCDMA (Code Division Multiple Access) system.

BACKGROUND ART

[0002] In a digital radio communication system, an interferencecanceller technology, which estimates a desired signal and interferencesignal based on maximum likelihood estimation, is used. There areinterference canceller systems in a CDMA system such as a single user(SUD: Single User Detection) type and multi-user (MUD: Multi UserDetection) type.

[0003] As the MUD, there are a multi-stage type interference cancellerthat improves a reception characteristic by repeating a plurality oftimes (multi-stage) processing on the receiving side of generatinginterference replica signals of other users based on channel estimatedvalues and decision data, subtracting these replica signals from areceived signal and thereby improving an SIR (Signal to InterferenceRatio), and a single-stage type interference canceller that improves areception characteristic by applying ranking processing to likelihood ofall symbols of all channels, generating replica signals for symbols indescending order of likelihood and subtracting the replica signals froma received signal on the receiving side and thereby improving an SIR.

[0004] A W-CDMA (Wideband-Code Division Multiple Access) of a digitalradio communication system is a system suitable for implementing amultimedia communication handling various transmission rates.Technologies concerning an application of an interference canceller tothis W-CDMA currently being developed and published by researchorganizations are technologies mainly applied to an uplink DPCH(Dedicated Physical CHannel).

[0005] That is, in an application of an interference canceller toW-CDMA, this technology creates replica signals from a received signalof DPDCH (Dedicated Physical Data CHannel) or DPCCH (Dedicated PhysicalControl CHannel) of other stations and subtracts those replica signalsfrom a total received signal and thereby cancels interference componentsfrom the received signals through demodulation at the own station. Thistechnology is intended to mainly implement a reduction of required Eb/No(SIR) of DPDCH by applying an interference canceller (MUD) to a basestation.

[0006] Even if replica signals are created using either DPDCHs or DPCCHsof other stations, this technology cancels interference among otherstations from the received signal only through demodulation of DPDCHs.This is because delays involved in the processing by an interferencecanceller of creating replica signals and subtracting the replicasignals from the received signal can be tolerated for DPDCHs more orless (about several frames).

[0007] For an interference canceller technology such as MUD, reducingnot only an amount of processing but also a processing delay is animportant issue in implementation. An actually reported demodulationdelay of DPDCH (data section) by an interference canceller is on theorder of several slots to several frames.

[0008] On the other hand, an allowable amount of delay of signalstransmitted with DPCCH is restricted a great deal. For example, in thecase where a slot configuration of an uplink signal is determined asshown in FIG. 1, that is, DPDCH is assigned to an in-phase component(Ich) and DPCCH is assigned to a quadrature component (Qch), it isstipulated for standardization as shown in FIG. 2 that the receivingside should change transmission power (indicated by arrow X in FIG. 2)from the first pilot signal immediately after a TPC bit is receivedaccording to a TPC (Transmission Power Control) bit for transmissionpower control. This allows a processing delay of only several tens ofμs. Furthermore, only a processing delay of not more than 1 slot isallowed for demodulation of FBI (FeedBack Information) which is acommand for transmission diversity or SSDT (Site Selection DiversityTransmission) or TFCI (Transport-Format Combination Indicator)indicating the type of communication quality such as a transmission rateand service depending on the purpose of use.

[0009] Therefore, demodulation of a DPCCH signal with such a smallamount of allowable processing delay needs to be processed beforecanceling interference or in the middle of cancellation of interference.Thus, unlike DPDCH, it is difficult to implement an improvement of aDPCCH reception characteristic by an interference canceller, that is, areduction of a required SIR or Eb/No, etc.

[0010] When such an interference canceller is introduced to a basestation, interference with the DPDCH is reduced as shown in FIG. 3, andtherefore it is possible to reduce transmission power of the DPDCH atthe communication terminal and reduce interference with other stations.Thus, by reducing the transmission power of the DPDCH it is alsopossible to reduce the transmission power of the DPCCH.

[0011] However, utilizing the effect (area indicated by broken line inFIG. 3) resulting from a reduction of the transmission power of theDPDCH at the communication terminal for increasing the system capacity,that is, utilizing the effect for additions of new users will result inan increase of interference corresponding to the additional users, whichrequires relatively more transmission power of the DPCCH, preventingtransmission power required for DPCCHs with a restricted demodulationdelay such as channel estimation and demodulation of a TPC command fromreducing.

[0012] Thus, as opposed to again factor (G) in transmitting DPDCHmultiplexed with DPCCH when no interference canceller is introduced,this gain factor changes a great deal when an interference canceller isintroduced to a base station.

[0013] An optimal gain factor depends on the capability of aninterference canceller, that is, interference cancellation performance,applicable channels (e.g., only applicable to a communication channel(DPCH) at a specific transmission rate), applicable parts (e.g., appliedto only DPDCH). Therefore, the optimal gain factor differs a great dealbetween a base station to which no interference canceller is applied anda base station to which an interference canceller is applied. Inaddition, the optimal gain factor may also differ between base stationsusing interference cancellers of different capabilities.

[0014] By the way, it is stipulated by 3GPP (3rd Generation PartnershipProject) that the value of this gain factor should be determined on thenetwork side (upper layer) and transmitted to the communication terminalside by a control signal.

[0015] On the other hand, transmission power control (power control) isconstructed of an inner loop which is controlled by a base station usinga target SIR as a base and an outer loop in which an RNC (Radio NetworkController) controls a target SIR using channel quality (bit error rate(BER) or a block error rate (BLER) as a base.

[0016] The value of the target SIR controlled by the RNC through theouter loop during diversity handover (Diversity Hand Over: DHO) iscontrolled as a value common to a plurality of base stations and as theonly value. This is because there is a premise that the SIR valuesatisfying required quality (BLER, etc.) does not vary drastically amonga plurality of base stations.

[0017] During diversity handover, a communication terminal communicateswith two base stations simultaneously. As described above, an optimalgain factor differs when the communication terminal is communicatingwith a base station with no interference canceller and whencommunicating with a base station with an interference canceller.Therefore, how to determine an optimal gain factor during diversityhandover when there is a difference between base stations with andwithout an interference canceller or between base stations withinterference cancellers of different capabilities is a question, but itis an actual situation that there is no technique to solve this problem.

[0018] Furthermore, when an interference canceller is introduced to abase station, the reception capability with respect to a target SIR,that is, a relationship between the SIR of DPCCH and the quality ofDPDCH (BER, BLER) is changed. Therefore, even if the measured value ofthe SIR of DPCCH is constant, the channel quality of DPDCH may varydepending on the demodulation capability (basic reception capability,presence/absence of an interference canceller or its interferencecancellation capability, etc.) of DPDCH of each base station.

[0019] Therefore, keeping the same relationship between the SIR of DPCCHand the quality of DPDCH (BER, BLER) for when an interference cancelleris introduced to a base station and when no interference canceller isintroduced to a base station requires the gain factor to be adjustedaccording to whether or not to use an interference canceller or thecapability of each interference canceller.

[0020] However, during diversity handover, a communication terminalsends a signal with DPDCH and DPCCH multiplexed made up of a common gainfactor. Thus, it is unavoidable that the relationship between the SIR ofDPCCH and the quality of DPDCH (BER, BLER) will vary from one basestation to another that receives the signal.

DISCLOSURE OF INVENTION

[0021] It is an object of the present invention to provide a radioinfrastructure apparatus capable of carrying out communications with anoptimal gain factor during diversity handover between base stations withand without an interference canceller or between base stations withdifferent reception capabilities with respect to a target SIR such asthe capabilities of interference cancellers and performing outer loopcontrol in such a way that there is no significant difference in thecommunication quality of DPDCH between base stations.

[0022] This object can be attained by correcting a target SIR using anadaptively controlled optimal gain factor, etc. and calculating anindependent SIR value for each base station.

BRIEF DESCRIPTION OF DRAWINGS

[0023]FIG. 1 illustrates a frame format of an uplink channel;

[0024]FIG. 2 illustrates transmission power control timing;

[0025]FIG. 3 illustrates a reception characteristic gain;

[0026]FIG. 4 is a block diagram showing a configuration of a radioinfrastructure apparatus according to Embodiment 1 of the presentinvention;

[0027]FIG. 5 is a block diagram showing a configuration of ademodulation section of the BTS of the radio infrastructure apparatusshown in FIG. 4;

[0028]FIG. 6 is a block diagram showing a configuration of acommunication terminal that carries out a radio communication with theradio infrastructure apparatus shown in FIG. 4;

[0029]FIG. 7 illustrates a non-DHO state of the radio infrastructureapparatus according to Embodiment 1;

[0030]FIG. 8 illustrates a DHO state of the radio infrastructureapparatus according to Embodiment 1;

[0031]FIG. 9 is a characteristic diagram showing a relationship betweenan error rate and target SIR;

[0032]FIG. 10 is a block diagram showing a configuration of a radioinfrastructure apparatus according to Embodiment 2 of the presentinvention;

[0033]FIG. 11 illustrates a DHO state of the radio infrastructureapparatus according to Embodiment 2;

[0034]FIG. 12 is a block diagram showing a configuration of a radioinfrastructure apparatus according to Embodiment 3 of the presentinvention; and

[0035]FIG. 13 is a block diagram showing another example of the HOcontrol section of the radio infrastructure apparatus shown in FIG. 12.

BEST METHOD FOR CARRYING OUT THE INVENTION

[0036] With reference now to the attached drawings, embodiments of thepresent invention will be explained in detail below.

[0037] (Embodiment 1)

[0038]FIG. 4 is a block diagram showing a configuration of a radioinfrastructure apparatus according to Embodiment 1 of the presentinvention. In FIG. 4, “BTS” denotes a base station and “RNC” denotes acontrol station. “Iub” denotes an interface. The radio infrastructureapparatus according to this embodiment adopts a configuration whereby atarget SIR is corrected inside the RNC.

[0039] First, the base station side will be explained. An uplink signalsent from a communication terminal with which the base station iscommunicating is received by radio section 102 via antenna 101. Radiosection 102 performs predetermined radio reception processing(down-conversion and A/D conversion, etc.) on the uplink signal andoutputs the signal after the radio reception processing to demodulationsection 103. Demodulation section 103 carries out processing such asdespreading processing, coherent detection, RAKE combining, channelCODEC and separation and is provided with an interference canceller.

[0040] Demodulation section 103 has a configuration shown in FIG. 5.Demodulation section 103 is a multi-stage type interference cancellerand is constructed of serially connected stages each including delayersand interference canceller units. Delay section 201 is a memory to delaya received signal for interference cancellers in each stage to carry outprocessing. Each stage creates a replica (S) for a signal, which becomesinterference and removes interference by subtracting this replica fromthe received signal. This allows demodulated data to be obtained with anSIR (signal to interference ratio) improved.

[0041] The interference canceller shown in FIG. 5 connects 1st stage 202and 2nd stage 203, but it is also possible to connect three or morestages to construct an interference canceller.

[0042] Each interference canceller is provided with a plurality ofprocessing lines and each processing line includes delayers 2021 and2031, subtractors 2022 and 2032, channel estimation and interferencegeneration units (hereinafter abbreviated as “CEIGU”) 2023 and 2033.There is no signal to be subtracted in the first processing line of 1ststage interference canceller 202, and so subtractor 2022 is notprovided.

[0043] Referring back to FIG. 4, the demodulated data obtained atdemodulation section 103 of the BTS is output to SIR measuring section104, where an SIR is measured using a known signal such as a pilotsection (PL) of the data. Furthermore, the demodulated data is output toerror detection section 109 and selection/combination section 113 of theRNC. Furthermore, demodulation section 103 outputs base stationinformation (information of demodulation capabilities) to G parametercontrol section 112 and SIR versus error rate estimation section 110.

[0044] The SIR value measured by SIR measuring section 104 is output toaddition section 105. A target SIR value for an inner loop is outputfrom the RNC to addition section 105 and addition section 105 calculateswhether the measured SIR value is higher or lower than the target SIRvalue. The difference information (whether the measured SIR value ishigher or lower than the target SIR value) is output to TPC commanddecision section 106.

[0045] TPC command decision section 106 decides and generates a TPCcommand for instructing an increase or decrease of transmission powerbased on the difference information. TPC command decision section 106then outputs the generated TPC command to multiplexing section 107.Multiplexing section 107 multiplexes the transmission data sent from theRNC and the TPC command and outputs the multiplexed signal to modulationsection 108. Modulation section 108 digital-modulates the multiplexedsignal and outputs the modulated signal to radio section 102. Modulationsection 108 carries out channel CODEC, digital modulation processing andspreading/modulation processing, etc.

[0046] Radio section 102 carries out predetermined radio transmissionprocessing (D/A conversion and up-conversion, etc.) on the modulatedsignal. This signal subjected to radio transmission processing is sentas a downlink signal through antenna 101 to a communication terminalwith which the base station is communicating.

[0047] Then, the control station side will be explained.Selection/combination section 113 that has received the demodulated datafrom the BTS also receives demodulated data from other BTSs and selectsdemodulated data with higher quality and outputs as received data. Thisreceived data is output to error detection section 114.

[0048] Furthermore, the received data is output to error detectionsection 114 and error detection section 114 calculates an error rate.The calculated error rate is output to addition section 115. A targeterror rate is output to addition section 115, where it is decidedwhether the calculated error rate is higher or lower than the targeterror rate. This decision result is output to target SIR control section116. Target SIR control section 116 controls the target SIR based on thedecision result.

[0049] On the other hand, the demodulated data from the BTS is alsooutput to error detection section 109. Error detection section 109carries out error detection using the demodulated data and outputs anerror rate such as BER and BLER to SIR versus error rate estimationsection 110. SIR versus error rate estimation section 110 estimates anSIR versus error rate using the error rate, target SIR value and Gparameter of the BTS, and demodulation capability of the BTS, etc. anddecides whether a correction of the target SIR value is necessary ornot.

[0050] For example, SIR versus error rate estimation section 110 storesthe characteristic of an SIR versus error rate to be a referencebeforehand, detects a difference between the SIR required to achieve asame error rate and the reference and decides, when the detected valueis larger, to correct by that value. Then, SIR versus error rateestimation section 110 outputs the decision result as to whether thetarget SIR value should be corrected or not and the amount of correctionto target SIR correction section 111.

[0051] More specifically, the amount of correction is determined using,for example, the characteristic diagram shown in FIG. 9. FIG. 9 showsthe SIR versus data section error rate characteristics of a BTS with nointerference canceller (normal BTS), and BTS1 and BTS2 (with differentinterference cancellation performances) with an interference canceller.The reference SIR versus error rate characteristic, that is, arelationship between the target SIR of the DPCCH base and the error rateof the data section (DPDCH) varies depending on the gain factor. Duringa correction, the reference SIR versus error rate characteristic (e.g.,normal BTS) is selected. The characteristic of the normal BTS is storedbeforehand for each optimal gain factor actually used or acquired asbase station information. Or a characteristic of a reference BTS at aspecific gain factor is stored or acquired beforehand, correctedaccording to the actual optimal gain factor and the correctedcharacteristic is stored or acquired as base station information. As thecorrection method, for example, a method of shifting the characteristicby y dB according to an amount of variation x in the gain factor can beused. Then, an amount of correction of the target SIR at each BTS isdetermined by detecting a difference between the SIR required to achievethe same error rate as that of the reference BTS and the reference(equivalent to amount of correction 1 or 2 in FIG. 9) using thedemodulation capability and the results of actual error ratemeasurements obtained beforehand as base station information and takinginto account the characteristics shown in IC-BTS1 and IC-BTS2 in FIG. 9.

[0052] Target SIR correction section 111 corrects the target SIR valuebased on the decision result from SIR versus error rate estimationsection 110 and the amount of correction thereof. The corrected targetSIR value is output to addition section 105 of the BTS. The target SIRvalues may be either corrected for their respective BTSs separately andoutput (to the respective BTS) or corrected for the respective BTSsseparately and then some of the target SIR values may be output to otherBTSs as common target SIR values.

[0053] Furthermore, the information on the demodulation capability ofthe BTS is output to G parameter control section 112 and G parametercontrol section 112 determines an optimal gain factor. The G parameterindicating the determined gain factor is output to multiplexing section107 of the BTS and multiplexed with the transmission data atmultiplexing section 107. Furthermore, the G parameter is output to SIRversus error rate estimation section 110.

[0054]FIG. 6 is a block diagram showing a configuration of acommunication terminal (MS) that carries out a radio communication withthe BTS. A downlink signal sent from the BTS with which thecommunication terminal is communicating is received by radio section 302through antenna 301. Radio section 302 carries out predetermined radioreception processing (down-conversion and A/D conversion, etc.) on thedownlink signal and outputs the signal after the radio receptionprocessing to demodulation section 303. Demodulation section 303 carriesout processing such as despreading processing, coherent detection, RAKEcombining, channel CODEC and separation.

[0055] Data demodulated by demodulation section 303 is obtained asreceived data and also output to TPC command extraction section 304. TPCcommand extraction section 304 extracts a TPC command and outputs theinstruction of the TPC command (for increasing or decreasingtransmission power) to an amplifier (not shown) of radio section 302.

[0056] Moreover, the demodulated data is output to G parameterrecognition section 305. G parameter recognition section 305 calculatesgain factors β d, β c corresponding to the G parameter from the BTS andmultiplies the transmission data by gain factors β d, β c. That is, thetransmission data of DPDCH (Ich) is output to multiplication section306, where the transmission data is multiplied by gain factor β d forDPDCH. The transmission data of DPCCH (Qch) is output to multiplicationsection 307, where the transmission data is multiplied by gain factor βc for DPCCH. The gains of DPDCH (Ich) and DPCCH (Qch) are adjusted inthis way.

[0057] The transmission data of DPDCH and DPCCH multiplied by gainfactors β d and β c are multiplexed by multiplexing section 308 and thenoutput to modulation section 309. Modulation section 309digital-modulates the multiplexed signal and outputs the modulatedsignal to radio section 302.

[0058] Radio section 302 carries out predetermined radio transmissionprocessing (D/A conversion and up-conversion, etc.) on the demodulatedsignal. This signal subjected to radio transmission processing is sentto the BTS with which the communication terminal is communicating as anuplink signal through antenna 301.

[0059] Then, an operation of the radio infrastructure apparatus in theabove-described configuration will be explained.

[0060] The infrastructure apparatus of the present invention sendsinformation such as the presence/absence of an interference canceller orreception capability from the BTS to the RNC, controls a G parameterindicating a gain factor and thereby determines an optimal gain factorduring diversity handover between base stations with and without aninterference canceller or between base stations with different receptioncapabilities with respect to target SIR value such as the capabilitiesof interference cancellers. Then, the infrastructure apparatus correctsthe target SIR (executes an outer loop) using the optimally adjustedgain factor, error rate, target error rate, etc.

[0061] Here, the gain factor (G) is intended to control the gain ratio(G parameter) of DPDCH to DPCCH of the uplink and varies from one TFC(Transport-Format Combination) to another. For example, at the highestrate, the gain factor may change from one radio frame to another. Thisgain factor may be signaled directly from the upper layer (network side)to an MS through a BTS or a reference value about reference TFC may besignaled to a BS through a BTS and the MS side may calculate the gainfactor based on the reference value as appropriate. The presentinvention is applicable to both cases likewise.

[0062] First, when diversity handover is not in progress (non-DHOstate), optimal gain factors are determined based on the receptioncapabilities of BTS1 and BTS2 as shown in FIG. 7 and sent to the MSthrough the respective BTSs as G parameters (G1, G2). The MS sends thetransmission data of DPDCH and DPCCH as an uplink signal to BTS1 or BTS2with which the MS is communicating using gain factors β d, β ccorresponding to the G parameters (G1, G2) received.

[0063] Furthermore, the target SIR value is corrected by the RNC basedon the gain factor, reception capabilities of the respective BTSs, errorrate measurement results of the respective BTSs and the corrected targetSIR values are sent to BTS1 and BTS2. BTS1 and BTS2 perform transmissionpower control of the inner loop using the corrected target SIR values.

[0064] Then, when diversity handover is in progress (DHO state), acommon optimal gain factor is determined based on the receptioncapabilities of BTS1 and BTS2 (DHO target BTSS) in the same way as thenon-DHO state as shown in FIG. 8 and sent as the G parameters to the MSthrough the respective BTSs. The MS sends the transmission data of DPDCHand DPCCH as an uplink signal to BTS1 and BTS2 with which the MS iscommunicating using gain factors β d, β c corresponding to the Gparameters received.

[0065] Furthermore, diversity handover takes place between BTSs with andwithout an interference canceller or between BTSs with differentreception capabilities, the relationship between the SIR of DPCCH andquality of DPDCH (BER, BLER) varies from one BTS to another, andtherefore the target SIR values are controlled for the respective BTSsseparately.

[0066] The target SIR value is corrected by the RNC based on the gainfactor, reception capabilities of the respective BTSs, error ratemeasurement results of the respective BTSs and the corrected target SIRvalues (target SIR1, target SIR2) are sent to BTS1 and BTS2. BTS1 andBTS2 perform transmission power control of the inner loop using thecorrected target SIR values (target SIR1, target SIR2).

[0067] In this way, when diversity handover takes place between BTSswith and without an interference canceller or between BTSs withdifferent reception capabilities, it is possible to decide a TPC commandin such a way that the BTSs have the same DPDCH reception quality.

[0068] Here, determination of a gain factor will be explained.Information on the demodulation capability of the BTS is output to Gparameter control section 112 in response to the uplink signal. Gparameter control section 112 determines an optimal gain factor based onthe number of BTSs connected, reception capability of each BTS, forexample, whether an interference canceller is incorporated or not,interference cancellation performance of the interference canceller,reception characteristic gain by the interference canceller (gain in thesystem capacity) or the error rate measurement result for each BTS, etc.

[0069] There is no problem with an optimal gain factor during diversityhandover between normal BTSs with no interference canceller, but how todetermine an optimal gain factor is a problem between one BTS with aninterference canceller and the other without an interference cancelleror between BTSs with interference cancellers of different interferencecancellation performances. That is, since the communication terminalneeds to perform transmission to both BTSs in the process of diversityhandover using one gain factor, the question is which BTS should be usedas a reference to determine the gain factor.

[0070] Thus, as described above, the gain factor is determined takinginto consideration the number of BTSs connected, reception capability ofeach BTS, for example, whether an interference canceller is incorporatedor not, interference cancellation performance of the interferencecanceller, reception characteristic gain of the interference canceller(gain in the system capacity) or the error rate measurement result foreach BTS, etc. In this case, the gain factor can be determined using anyBTS as a reference or a new optimal gain factor can be determined takinginto consideration the situation of any BTS.

[0071] There is no particular restriction on determination of an optimalgain factor as it is performed according to each of or a combination offactors like the number of BTSs connected, reception capability of eachBTS, for example, whether an interference canceller is incorporated ornot, interference cancellation performance of the interferencecanceller, reception characteristic gain of the interference canceller(gain in the system capacity) or the error rate measurement result foreach BTS, etc.

[0072] Then, correction of a target SIR value will be explained. Theerror rate measurement result of each BTS obtained from the demodulateddata is output to SIR versus error rate estimation section 110. SIRversus error rate estimation section 110 calculates an amount ofcorrection of the target SIR taking into consideration the number ofBTSs connected, reception capability of each BTS, for example, whetheran interference canceller is incorporated or not, interferencecancellation performance of the interference canceller, receptioncharacteristic gain of the interference canceller (gain in the systemcapacity), etc.

[0073] More specifically, when an amount of correction of the target SIRis calculated based on the error rate measurement result, for example,the characteristic diagram shown in FIG. 9 is used. In FIG. 9, an amountof correction is calculated from the value of an error rate of DPDCH ofeach BTS with reference to the characteristic line. For example, whendiversity handover takes place between a normal BTS and BTS1, the amountof correction of the target SIR (DPCCH base) is assumed to be amount ofcorrection 1 to achieve a required error rate 10⁻². On the other hand,when diversity handover takes place between a normal BTS and BTS2, theamount of correction of the target SIR is assumed to be amount ofcorrection 2 to achieve a required error rate 10⁻².

[0074] Thus, unlike the gain factor, the amount of correction of atarget SIR can be determined individually according to the actualsituation of the BTS. Even when diversity handover takes place betweenBTSs with different capabilities, this makes it possible to performappropriate transmission power control over the inner loop according tothe actual situation.

[0075] There is no particular restriction on determination of an amountof correction of a target SIR as it is carried out according to each ofor a combination of factors like reception capability of each BTS, forexample, whether an interference canceller is incorporated or not,interference cancellation performance of the interference canceller,reception characteristic gain of the interference canceller (gain in thesystem capacity), target SIR value, gain factor or the error ratemeasurement result for each BTS, etc.

[0076] Thus, the radio infrastructure apparatus according to thisembodiment controls a gain factor and target SIR value taking intoconsideration the reception capabilities of base stations, etc. and canthereby perform communications with an optimal gain factor takingadvantage of effects of interference cancellers and withoutdeteriorating the reception capabilities of base stations when diversityhandover takes place between base stations with and without aninterference canceller or between base stations with different receptioncapabilities.

[0077] When the RNC corrects a target SIR, the base station can controlwith the target SIR specified by the RNC, and thereby reduce the burdenon the base station apparatus. When many base stations are installed, itis necessary to reduce the cost and size of each base station, andtherefore such a configuration is preferred.

[0078] (Embodiment 2)

[0079]FIG. 10 is a block diagram showing a configuration of a radioinfrastructure apparatus according to Embodiment 2 of the presentinvention. In FIG. 10, “BTS” denotes abase station and “RNC” denotes acontrol station. “Iub” denotes an interface. In FIG. 10, the samecomponents as those in FIG. 4 are assigned the same reference numeralsas those in FIG. 4 and detailed explanations thereof will be omitted.The radio infrastructure apparatus according to this embodiment adopts aconfiguration whereby a target SIR is corrected inside the BTS.

[0080] In the radio infrastructure apparatus shown in FIG. 10, the BTSoutputs demodulated data to error detection section 109. Error detectionsection 109 carries out error detection using the demodulated data andoutputs error rates such as BER and BLER to SIR versus error rateestimation section 110. SIR versus error rate estimation section 110estimates an SIR versus error rate using the error rate, target SIRvalue, G parameter of each BTS, and demodulation capability of each BTS,etc. and decides whether a correction of the target SIR value isnecessary or not. Then, SIR versus error rate estimation section 110outputs the decision result as to whether the target SIR value should becorrected or not to target SIR correction section 111.

[0081] Target SIR correction section 111 corrects the target SIR valuebased on the decision result from SIR versus error rate estimationsection 110. The corrected target SIR value is output to additionsection 105 of the BTS.

[0082] Then, an operation of the radio infrastructure apparatus in theabove-described configuration will be explained.

[0083] In the case of a non-DHO state, a common gain factor specified bythe RNC is sent to BTS1 or BTS2 and BTS1 or BTS2 determines an optimalgain factor based on reception capabilities, etc. and sends the optimalgain factor as G parameters (G1, G2) to an MS through each BTS. The MSsends the transmission data of DPDCH and DPCCH as an uplink signal toBTS1 or BTS2 with which the MS is communicating using gain factors β d,β c corresponding to the G parameters (G1, G2) received.

[0084] With regard to the target SIR value, the target SIR valuecommonly controlled by the RNC is sent to BTS1 or BTS2 and corrected byBTS1 or BTS2 based on the gain factor, reception capabilities of therespective BTSs, error rate measurement results of the respective BTSs.BTS1 and BTS2 perform transmission power control over the inner loopusing the corrected target SIR values (target SIR1, target SIR2).

[0085] Then, in a DHO state, the common gain factor specified by the RNCis sent to BTS1 and BTS2 as shown in FIG. 11 and sent to the MS throughthe respective BTSs. The MS sends the transmission data of DPDCH andDPCCH as uplink signals to BTS1 and BTS2 with which the MS iscommunicating using gain factors β d, β c corresponding to the Gparameters received.

[0086] With regard to the target SIR value, the target SIR valuecommonly controlled by the RNC is sent to BTS1, and BTS2 and BTS1 andBTS2 correct the target SIR value based on the gain factor, receptioncapabilities of the respective BTSs, error rate measurement results ofthe respective BTSs and perform transmission power control over theinner loop using the corrected target SIR values (target SIR1, targetSIR2).

[0087] In this way, when diversity handover takes place between BTSswith or without an interference canceller or between BTSs with differentcapabilities, it is possible to decide a TPC command in such a way thatthe BTSs have the same DPDCH reception quality.

[0088] Thus, since the radio infrastructure apparatus according to thisembodiment also controls a gain factor and target SIR value taking intoconsideration the reception capabilities of base stations, etc. andtherefore it is possible to perform communications with an optimal gainfactor taking advantage of the effects of the interference cancellerswithout deteriorating the reception capabilities of the base stationsduring diversity handover between base stations with and without aninterference canceller or between base stations with interferencecancellers of different capabilities.

[0089] When the base station corrects a target SIR, the RNC only needsto transmit a conventional common target SIR to a plurality of basestations during DHO in the same way as the conventional art, and evenwhen an interference canceller is introduced to a specific base stationlater, there is no need to change the configuration of the RNC a greatdeal. Since the base station can perform control with the target SIRindividually according to the own reception capability or the amount ofchange of reception capability by introduction of an interferencecanceller, it is possible to reduce the burden on the RNC such asadditions of functions. This configuration is preferred when anapparatus is added for drastically improving the reception capabilityfor the target SIR value, for example, by only introducing aninterference canceller to a base station of some specific area, not allareas under the control of one RNC.

[0090] (Embodiment 3)

[0091] This embodiment will describe a case where a handover (HO)algorithm and its decision parameter, etc. are adaptively controlledaccording to a selection situation of an optimal gain factor and adifference in reception capability between BTSs.

[0092]FIG. 12 is a block diagram showing a configuration of a radioinfrastructure apparatus according to Embodiment 3 of the presentinvention. In FIG. 12, the same components as those in FIG. 4 areassigned the same reference numerals as those in FIG. 4 and detailedexplanations thereof will be omitted.

[0093] The radio infrastructure apparatus shown in FIG. 12 is providedwith HO control section 117 that controls a handover algorithm anddecision parameter thereof, etc. based on the G parameter determined bythe G parameter control section. This HO control section 117 includesselection situation confirmation section 1171 that confirms the gainfactor selection situation based on a G parameter entered and HOalgorithm change section 1172 that changes the HO algorithm based on theconfirmation result of the selection situation.

[0094] The operation of the radio infrastructure apparatus in theabove-described configuration is the same as that of Embodiment 1 exceptthe control for changing the HO algorithm using the G parameter.Selection situation confirmation section 1171 confirms whether the Gparameter selected by G parameter control section 112 is significantlydifferent from the optimal gain factor at each BTS or not. The specificmethod for confirmation can be performed through threshold decision foran optimal gain factor, etc.

[0095] When the G parameter selected at a BTS is significantly differentfrom the optimal gain factor, a control signal indicating thatdifference is transmitted to HO algorithm change section 1172 and the HOalgorithm is changed. By the way, there is no particular restriction onthe HO algorithm to be changed.

[0096] For example, for diversity handover between a BTS with aninterference canceller and another BTS with no interference canceller,it is basically desirable to determine a gain factor according to theBTS with no interference canceller (normal BTS) in order to performfavorable demodulation of DPDCH.

[0097] This is because, when a communication is performed with a gainfactor according to the BTS with a canceller, the reception power of thedata section of normal BTS is too small to perform correct demodulationfor the SIR suitable for reception of DPCCH. Furthermore, when anattempt is made to correct the target SIR according to the error rate ofthe data section and increase the reception power, not onlycommunication quality of DPCCH becomes excessive, but also thecommunication terminal performs transmission excessively, which causesgreat interference with the system and causes large power consumption ofthe battery.

[0098] However, with the gain factor adapted to such a normal BTS, it isnot possible to take advantage of the effects of extension of servicelife of the terminal due to a reduction of DPDCH transmission powerobtained by the introduction of the interference canceller or increaseof the system capacity by the reduction of the amount of interference bya reduction of transmission power.

[0099] Thus, when diversity handover takes place between a normal BTSand a BTS with an interference canceller, the algorithm is changed to anHO algorithm that will cut the channel for the normal BTS ahead of time.Based on the changed HO algorithm, the RNC carries out HO control overthe communication terminal.

[0100] Thus, the radio infrastructure apparatus according to thisembodiment controls a gain factor and target SIR value taking intoconsideration the reception capabilities of base stations, and thereforeduring diversity handover between base stations with and without aninterference canceller or between base stations with interferencecancellers of different reception capabilities, the radio infrastructureapparatus can not only perform communications taking advantage of theeffects of the interference canceller without deteriorating thereception capabilities of base stations and with an optimal gain factorbut also adaptively control the HO algorithm and its decision parameter,etc. according to the optimal gain factor selection situation anddifference in reception capability between BTSs and make full use of theeffects of introducing the interference canceller.

[0101] In this embodiment, HO control section 117 can also beconstructed of reception capability difference decision section 1173that decides a difference in reception capability between BTSs and HOalgorithm change section 1172 as shown in FIG. 13 and the HO algorithmcan be changed when there are great differences in reception capabilitybetween BTSs notified from the higher layer. The effects of thisembodiment can be fully exploited in this case, too.

[0102] The present invention is not limited to foregoing Embodiments 1to 3, but can be implemented with various modifications. For example,foregoing Embodiments 1 to 3 describe the case where an MUD is used asthe interference canceller, but the present invention is also applicableto cases where an SUD or symbol ranking type interference canceller isused as the interference canceller.

[0103] Furthermore, foregoing Embodiments 1 to 3 have described the casewhere modulation processing is carried out after data is multiplexed,but the present invention has no particular restrictions on the sequenceof data multiplexing (frame assembly) and channel CODEC and data canalso be multiplexed after modulation processing is carried out.

[0104] As described above, the radio infrastructure apparatus of thepresent invention controls a gain factor and target SIR value takinginto consideration reception capabilities of base stations, etc. andtherefore during diversity handover between base stations with andwithout an interference canceller or between base stations withdifferent reception capabilities with respect to target SIR values suchas capabilities of interference cancellers, the radio infrastructureapparatus can not only perform communications taking advantage of theeffects of the interference canceller without deteriorating thereception capabilities of base stations and with an optimal gain factor.

[0105] This application is based on the Japanese Patent ApplicationNo.2000-363621 filed on Nov. 29, 2000, entire content of which isexpressly incorporated by reference herein.

[0106] Industrial Applicability

[0107] The present invention is ideally applicable to a digital radiocommunication system and a radio infrastructure apparatus in a CDMA(Code Division Multiple Access) system in particular.

What is claimed is:
 1. A radio infrastructure apparatus comprising: abase station apparatus provided with a measuring section that measures asignal to interference ratio using an uplink signal made up of a datachannel code-multiplexed with a control channel and a transmission powercontrol section that generates a transmission power control signal fromsaid signal to interference ratio and a target signal to interferenceratio; and a control station provided with a control section thatcontrols gain factors corresponding to said data channel and saidcontrol channel based on base station information from each basestation, a control section that controls said target signal tointerference ratio and a correction section that corrects said targetsignal to interference ratio using said base station information andsaid gain factors.
 2. The radio infrastructure apparatus according toclaim 1, wherein when no diversity handover is in progress, the controlsection controls the gain factors based on the base station informationand the correction section corrects the target signal to interferenceratio based on said base station information.
 3. The radioinfrastructure apparatus according to claim 1, wherein when diversityhandover is in progress, the control section determines a common gainfactor based on the base station information and the correction sectioncorrects the target signal to interference ratio for each handovertarget base station individually based on said base station information.4. A radio infrastructure apparatus comprising: a base station apparatusprovided with a measuring section that measures a signal to interferenceratio using an uplink signal made up of a data channel code-multiplexedwith a control channel, a transmission power control section thatgenerates a transmission power control signal from said signal tointerference ratio and a target signal to interference ratio and acorrection section that corrects said target signal to interferenceratio using said base station information and said gain factorscorresponding to said data channel and said control channel; and acontrol station provided with a control section that controls saidtarget signal to interference ratio and a control section that controlsthe gain factors based on the base station information from each basestation.
 5. The radio infrastructure apparatus according to claim 1,wherein the gain factors are controlled using at least one parameterselected from a group of parameters that are parameters, namely thenumber of base stations connected, reception capability of each basestation or the error rate measurement result for each base station. 6.The radio infrastructure apparatus according to claim 1, wherein thebase station information is at least one selected from a group ofreception capabilities and error rate measurement results of the basestation apparatuses.
 7. The radio infrastructure apparatus according toclaim 1, wherein the reception capability consists of thepresence/absence of an interference canceller, reception characteristicgain, difference in the degree of improvement of receptioncharacteristics of the data channel and control channel or the range ofa channel to which the interference canceller is applied and the numberof channels.
 8. The radio infrastructure apparatus according to claim 1,wherein the target signal to interference ratio is corrected using atleast one parameter selected from a group of parameters of base stationinformation, gain factors corresponding to the data channel and controlchannel, common target signal to interference ratio and error ratemeasurement result of each base station.
 9. The radio infrastructureapparatus according to claim 1, further comprising a handover controlsection that changes a handover algorithm or the decision parameter,according to a gain factor selection situation and differences in basestation information between the target base stations.
 10. A radio basestation apparatus comprising a transmission section for transmittinggain factors determined by the radio infrastructure apparatus accordingto claim 1 to a communication terminal apparatus.
 11. A communicationterminal apparatus comprising: a gain adjustment section that adjuststhe gains of a data channel and control channel using the gain factorsdetermined by the radio infrastructure apparatus according to claim 1;and a multiplexing section that code-multiplexes the data channel andcontrol channel whose gains have been adjusted.
 12. A gain factorcontrol method comprising the steps at a base station apparatus of:measuring a signal to interference ratio using an uplink signal made upof a data channel code-multiplexed with a control channel; andgenerating a transmission power control signal from said signal tointerference ratio and a target signal to interference ratio, and thesteps at a control station of: controlling gain factors corresponding tosaid data channel and said control channel based on base stationinformation from each base station; controlling said signal tointerference ratio; and correcting said target signal to interferenceratio using said base station information and said gain factors.
 13. Again factor control method comprising the steps at a base stationapparatus of: measuring a signal to interference ratio using an uplinksignal made up of a data channel code-multiplexed with a controlchannel; generating a transmission power control signal from said signalto interference ratio and a target signal to interference ratio; andcorrecting said target signal to interference ratio using the basestation information and said gain factors corresponding to said datachannel and said control channel, and the steps at a control station of:controlling said target signal to interference ratio; and controllingthe gain factors based on base station information from each basestation.